Puccinia is a genus of fungi that is harmful to plants. For example, Puccinia triticina causes leaf rust, a prevalent disease of wheat. One of the worst parts of this infection is that it can cause a loss of 20% of the harvest. It happens because in warm climates, pathogen overwinters easily, and also rotten leaves worsen the situation because they fertilize the fungus. As long as the infected leaf is alive, the fungus can spread further because wind can transfer infectious urediniospores, so even plants hundreds of kilometers away can be affected. Puccinia graminis, also known as black stem rust, affects cereals. It is the primary host for wheat and the barberry plant.